OP: Your gut will tell you if it'll be a good move to go from the M3 to the ZHP. You may miss the limited slip (depends on how hard you drive). You will miss the power. Brakes and handling are not all that different in everyday driving. The M3 does feel slightly more nose heavy (due to the beastly motor) if both are on the track, but the LSD definitely helps make up for that. The gas mileage is not all that close: 16-18 vs 21-25 in my experience. The sound and feel of the two cars is very, very different and is also subjective.
Both are very nice cars built for different purposes.
And of course part of this thread had to turn into a bickering match. I don't think suspensions are blown at 50k, some may not even be completely shot at 100k. There is no doubt that they aren't "good as new" at that point though. The struts I removed from my zhp (330 sport shocks) at 105k rebounded perfectly. They were not blown. I'm sure they weren't up to original operating performance though.
Now in contrast, I remember fiveightandten bought new Sachs shocks for his E36 M3 and IIRC some were leaking before he even had 15k miles or so on them.
Also, not all Sachs shocks are created equal. The earlier E46s with the sport package have a better built Sachs dampers that are part of a different class of Sachs dampers, and will last longer than those in the newer E46s. That doesn't apply to early E46 non-sports though.
Last edited by Grande D; 11-30-2012 at 02:59 PM.